There was nothing floating around inside the head. Judging by the way it looks, I'm leaning towards the cap not being present. Not sure how that could have happened though, unless it wasn't present from the time I got it back from the machinist.

I tore that head off in record time, but not quick enough to get to the shop before they close.

Just to satisfy my curiosity, and since the lash caps look just like what is in the photo on your intake valve, would you check to see if that is a cap on there, or not? It should just pull right off with a pair of needle-nose pliers, without any damage.

If there are no lash caps anywhere to be found, then it was assembled without lash caps, and that's what caused it.

If there is a lash cap on the intake, and not on the exhaust, then that could be the reason why the exhaust failed. Or perhaps the exhaust lash cap broke apart. I have seen them severely damaged on the top before, but never actually coming apart. But it could happen.

Interesting problem. Just replaced the rocker assemblies in my bullet. In my case I did not remove or replace the valve stem caps shown in the last picture. Did not look like there was much wear there and the rockers themselves did not have the same wear as shown in the picture for the exhaust valve. In my case the rockers were not getting oil, so the bearing surface was completely worn out and the shafts had lateral movement. It certainly appears that the cap was simply issuing on the exhaust valve.

I am wondering now if I should have replaced the caps when I did my rocker assemblies?Duncan

If they looked ok with only light contact marks then I am sure the valve stem caps will be fine.

My experience is that the caps can be very difficult to remove once they have been run for a few thousand miles. I think the soft valve stem grows into them. The last two times, I have had to resort to taking out the retaining collets with the caps in place, letting valve spring pressure (and taps with a soft hammer) drive the caps off into a containing sack. No way could I get them off by just pulling on them, even though they did not have an excessively tight fit when I installed them.

Chas is correct on the caps last time I used a little heat and they came right off. ERC

Well, I yanked on the end of that intake valve for a while with pliers, and tried to pry it from the side. It hardly has any miles on it. So it seems like there's no cap on there to me. Odd that the intake would survive and not the exhaust though. The intake valve is way softer metal than the exhaust.